The present invention relates to expandable intraluminal grafts (xe2x80x9cstentsxe2x80x9d) for use within a body passageway or duct which are particularly useful for repairing blood vessels narrowed or occluded by disease. The present invention relates even further to such stents having helically wound hoops.
Various endoprosthesis assemblies which include expandable stents have been proposed or developed for use in association with angioplasty treatments and other medical procedures. The endoprosthesis assembly is percutaneously routed to a treatment site and the stent is expanded to maintain or restore the patency of a body passageway such as a blood vessel. A stent is typically cylindrical in shape comprising an expandable open frame. The stent will typically expand either by itself (self-expanding stents) or will expand upon exertion of an outwardly directed radial force on an inner surface of the stent frame by a balloon catheter or the like.
Stents for endovascular implantation into a blood vessel, artery or the like to maintain or restore the patency of the passageway have been deployed percutaneously to minimize the invasiveness associated with surgical exposure of the treatment site during coronary artery bypass. Percutaneous deployment is initiated by an incision into the vascular system of the patient, typically into the femoral artery. A tubular or sheath portion of an introducer is inserted through the incision and extends into the artery. The introducer has a central lumen which provides a passageway through the patient""s skin and artery wall into the interior of the artery. An outwardly tapered hub portion of the introducer remains outside the patient""s body to prevent blood from leaking out of the artery along the outside of the sheath. The introducer lumen includes a valve to block blood flow out of the artery through the introducer passageway. A distal end of a guide wire is passed through the introducer passageway into the patient""s vasculature. The guide wire is threaded through the vasculature until the inserted distal end extends just beyond the treatment site. The proximal end of the guide wire extends outside the introducer.
For endovascular deployment, a stent, in an unexpanded or constricted configuration, is crimped onto a deflated balloon portion of a balloon catheter. The balloon portion is normally disposed near a distal end of the balloon catheter. The catheter has a central lumen extending its entire length. The distal end of the balloon catheter is threaded onto the proximal end of the guide wire. The distal end of the catheter is inserted into the introducer lumen and the catheter is pushed along the guide wire until the stent reaches the treatment site. At the treatment site, the balloon is inflated causing the stent to radially expand and assume an expanded configuration. When the stent is used to reinforce a portion of the blood vessel wall, the stent is expanded such that its outer diameter is approximately 10% to 20% larger than the inner diameter of the blood vessel at the treatment site, effectively causing an interference fit between the stent and the blood vessel that inhibits migration of the stent. The balloon is deflated and the balloon catheter is withdrawn from the patient""s body. The guide wire is similarly removed. Finally, the introducer is removed from the artery.
An example of a commonly used stent is given in U.S. Pat, 4,733,665 filed by Palmaz on Nov. 7, 1985, which is hereby incorporated herein by reference. Such stents are often referred to as balloon expandable stents. Typically the stent is made from a solid tube of stainless steel. Thereafter, a series of cuts are made in the wall of the stent. The stent has a first smaller diameter which permits the stent to be delivered through the human vasculature by being crimped onto a balloon catheter. The stent also has a second, expanded diameter, upon the application, by the balloon catheter, from the interior of the tubular shaped member of a radially, outwardly extending force.
Other types of stents known in the art are often referred to as self expanding stents, which act like springs and will recover to their expanded or implanted configuration after being crushed. The prior art makes reference to the use of alloys such as Nitinol (Nixe2x80x94Ti alloy) which have shape memory and/or superelastic characteristics in medical devices which are designed to be inserted into a patient""s body. The shape memory characteristics allow the devices to be deformed to facilitate their insertion into a body lumen or cavity and then be heated within the body so that the device returns to its original shape. Superelastic characteristics on the other hand generally allow the metal to be deformed and restrained in the deformed condition to facilitate the insertion of the medical device containing the metal into a patient""s body, with such deformation causing the phase transformation. Once within the body lumen the restraint on the superelastic member can be removed, thereby reducing the stress therein so that the superelastic member can return to its original un-deformed shape by the transformation back to the original phase.
One particular type of stent is often referred to as a helical stent, an example of which can be found in U.S. Pat. No. 5,913,897 issued to Corso et al. on Jun. 22, 1999, which is hereby incorporated herein by reference. A typical helical stent, such as the one disclosed in the Corso et al. reference, is made by either cutting a pattern from a solid tube or winding a wire around a mandrel. The tubular member has a plurality of adjacent helically aligned hoops extending between the front and back ends of the stent. The hoops are formed of a plurality of longitudinal struts, each having opposing ends and a center therebetween. The ends of the struts are shaped to form a plurality of loops, which connect adjacent struts at the ends of the struts. The stent further includes a plurality of bridges connecting adjacent hoops to one another. The endoprosthesis body is thus composed of a plurality of full-circle undulating hoops continuous with each other along the helical path. In general, the undulations of adjoining full circle hoops generally line up with one another to either contact one another or be closely spaced from one another. At selected ones of these locations, bridges are provided in order to join adjacent hoops. In the Corso et el. device, at least one bridge is positioned along each full-circle section, and the bridges are oriented with respect to each other so as to form a helical pattern of bridges along the endoprosthesis.
One disadvantage with prior art helical stents, is that the ends of the stent are not flat. That is, the end of the stent did not lie in a single plane substantially perpendicular to the longitudinal axis of the stent. The angled or beveled end configuration of the stent could result in a lift-up of the end loops while the stent is being delivered through very angled vessel curvatures. The lift-up could scrape the vessel wall causing injury to the vessel wall, or could prevent the stent from being advanced into the target area. Equally, the stent""s proximal end could hang up upon retraction into the guide catheter, thus causing the stent to embolize.
In accordance with the present invention, there is provided a stent for insertion into a vessel of a patient. The stent is a tubular member having a thickness and having front and back open ends and a longitudinal axis extending therebetween. The member has a first smaller diameter for insertion into the vessel, and a second larger diameter for deployment into the vessel. The tubular member includes a plurality of helically oriented continuous adjacent hoops extending between the front and back ends. The hoops have a plurality of longitudinal struts each having opposing ends and a center therebetween, wherein the ends of the struts are shaped to form a plurality of loops connecting adjacent struts at the ends of the struts. The tubular member has end loops at the front and back ends thereof, wherein the end loops at each end are substantially aligned with each other along a plane substantially perpendicular to the longitudinal axis.